Relay-tripping system



. Aug. 14, 1928.

L. N. CRICHTON ET AL RELAY 'IRIPPING SYSTEM Filed May 24. 1921 w d Rm 00m mfi ECR V 0 M e e c h n 5 6V Mr W a L AONE Patented Aug. 14, 1928.

UNITED STATES PATENT OFFICE nnsnm N. 'cnrcn'ron, or nnenwoon, armLAWRENCE n. GOLLADAY, or wmxms- BURQ}, PENNSYLVANIA, ASSIGNOBS TO-WES'1INGHOUSE ELECTR IC AND MANUFAC- TUBING comm, A conromrron orrannsnvamn.

nnnaY-rmrrme srsrau.

Application filed Kay 24,

Another object of'our invention is to vide a relay system, oftheabove-indicated character, that shall co-operate with a currenttransformer, energized from the circuit to be protected, in such mannerthat normally'no load will be placed upon the current transformer butenergy will be derived therefrom to ener 'ze a trip coil only upon theoccurrence of predetermined abnormal conditions. i

Another objectof our invention is to provide a relay tripping system, ofthe aboveindicated character, that shall embody a resonant circuitwhereby normally no load will be placed upon the-current transformeruntil the predetermined abnormal conditions occur, whereupon the tricoil will be connected to an element ,of t e resonant circuit in suchmanner as to be energized from the current transformer. I

A further object of ourinvention is to provide a relay tripping-systemof the aboveindicated character thatshall be simple in arrangement andeffective in its operatlon.

In systems heretofore employed for deriving-tripping energy from acurrent transformer to be protected,"v arious devices have been employedto control the connection of a. trip coil to the current transformerupon the occurrence of redetermined abnormal conditions. Such eviceshave been so disposed as to be continuously energized, and a load'wasthus always-placed upon the cur-' .renttransform'er.

Inview of that condition, a system embodying our invention comprises aresonant circuit including a current transformer, a condensive reactorand an inductive reactor. Although the potential difierence'across theterminals of either reactor might be relatively large, the load on thecurrent transformer and, consequently, the potential dif- 1921 Serialll'o. 472,151,

nect the trip coil of a circuit interrupter across the terminals ofeither reactor upon the occurre cc of predetermined abnormal conditions,it'ective protection of the circuit may be obtained, and actuatingenergy for the interrupter may be derived from the circuit to beprotected without placing a continuous load upon the currenttransformer; In such a system, the elimination of the load placed uponthe current transformer by, the controlling devices would liU rendermeasuring instruments connected to the current transformer more accuateby reason of thelesser load on the transformer. The accompanymg drawingis a diagrammatic view of a relay trippmg system embodying ourinvention.

Referring to the drawing, a source 1 of electromotive force suppliesenergy to a circuit 2 through a. circuit interrupter 3. Upon theoccurrence of abnormal conditions in the circuit 2, such asextremeoverload or shortcircuit, the interrupter 3 is adapted to beactuated by a tripping mechanism 4, the energization of which'iscontrolled by a relay tripping system 5. v Y

The relay system 5 comprises the secondary winding 6 of a currenttransformer 7, the primary winding 8 of which is connected in themainicirc-uit. The secondary winding 6 of the current transformer isconnected in circuit with the winding of an electrical instrument 9, thefwindin ;of a relay 10, an inductive reactor 11 an a condensive -re-.actpr 12.1

- The relay 10 is preferably. of the induction disc type embodying-aninverse tinieelement and, when energized to a predetermined degree, isadapted toeffect the enga ement of apair of contactmembers 13 and 14..The instrument 9 and the relay 10 serve to increase the value ofinductive reactance of the relay system, and, if desired, may bearranged to constitute the entire inductive reactance.

"1 The reactive elements 9, 10, 11 and 12 are circuit therewith that thecircuit normally is rendered resonant. Upon the occurrence of suchabnormal conditions in the load circuit 2 as suffice to efiect theengagement of the contact members 13 and 14, the trip coil 4 isconnectedacross-the condensive reactor 12, whereupon the resonantcondition of thecircuitis disturbed and suflicient energy is thereuponderived from the main circuit,

through the current transformer 7, to energize the trip coil 4:.

It will be observed that, until the resonant condition is disturbed bythe connection of the trip coil across'the terminals of the condensivereactor 12, no load is placed upon the current transformer except'by themeasuring instrument 9 and the relay 10. In the system illustrated, theinductive reactance of the instrument 9 and of the relay 10 contributeto the inductive reactance-of the resonant circuit.

'It will thus be observed that substantially no load is normally placedupon the current transformer by auxiliary control devices which areemployed to provide a potential difference for energizing the trip coil,but only upon the occurrence of predetermined abnormal conditions, suchas overloads of predetermined values, or short-circuits-will a largeload be placed upon the current transformer.

It is understood that various other arrangements of the elementsdescribed and illustrated may be made within the spirit and scope of theinvention, as set forth in the appended'claim.

We claim as our invention:

In an electric circuit, the combination with a circuit-interrupterprovided with a* trip coil controlling said circuit, of a currenttransformer connected in said circuit, a relay, a winding for said relayand a condenser connected in series with the secondary wind-- subscribedour names this 11th day of May,

LESLIE N. CRICHTON. LAWRENCE R. GOLLADAY-

